Archipelago » qemu

/*

 * General purpose implementation of a simple periodic countdown timer.

 *

 * Copyright (c) 2007 CodeSourcery.

 *

 * This code is licensed under the GNU LGPL.

 */

#include "hw.h"

#include "qemu-timer.h"

#include "ptimer.h"

#include "host-utils.h"

struct ptimer_state

{

    uint8_t enabled; /* 0 = disabled, 1 = periodic, 2 = oneshot.  */

    uint64_t limit;

    uint64_t delta;

    uint32_t period_frac;

    int64_t period;

    int64_t last_event;

    int64_t next_event;

    QEMUBH *bh;

    QEMUTimer *timer;

};

/* Use a bottom-half routine to avoid reentrancy issues.  */

static void ptimer_trigger(ptimer_state *s)

{

    if (s->bh) {

        qemu_bh_schedule(s->bh);

    }

}

static void ptimer_reload(ptimer_state *s)

{

    if (s->delta == 0) {

        ptimer_trigger(s);

        s->delta = s->limit;

    }

    if (s->delta == 0 || s->period == 0) {

        fprintf(stderr, "Timer with period zero, disabling\n");

        s->enabled = 0;

        return;

    }

    s->last_event = s->next_event;

    s->next_event = s->last_event + s->delta * s->period;

    if (s->period_frac) {

        s->next_event += ((int64_t)s->period_frac * s->delta) >> 32;

    }

    qemu_mod_timer(s->timer, s->next_event);

}

static void ptimer_tick(void *opaque)

{

    ptimer_state *s = (ptimer_state *)opaque;

    ptimer_trigger(s);

    s->delta = 0;

    if (s->enabled == 2) {

        s->enabled = 0;

    } else {

        ptimer_reload(s);

    }

}

uint64_t ptimer_get_count(ptimer_state *s)

{

    int64_t now;

    uint64_t counter;

    if (s->enabled) {

        now = qemu_get_clock_ns(vm_clock);

        /* Figure out the current counter value.  */

        if (now - s->next_event > 0

            || s->period == 0) {

            /* Prevent timer underflowing if it should already have

               triggered.  */

            counter = 0;

        } else {

            uint64_t rem;

            uint64_t div;

            int clz1, clz2;

            int shift;

            /* We need to divide time by period, where time is stored in

               rem (64-bit integer) and period is stored in period/period_frac

               (64.32 fixed point).

               Doing full precision division is hard, so scale values and

               do a 64-bit division.  The result should be rounded down,

               so that the rounding error never causes the timer to go

               backwards.

            */

            rem = s->next_event - now;

            div = s->period;

            clz1 = clz64(rem);

            clz2 = clz64(div);

            shift = clz1 < clz2 ? clz1 : clz2;

            rem <<= shift;

            div <<= shift;

            if (shift >= 32) {

                div |= ((uint64_t)s->period_frac << (shift - 32));

            } else {

                if (shift != 0)

                    div |= (s->period_frac >> (32 - shift));

                /* Look at remaining bits of period_frac and round div up if 

                   necessary.  */

                if ((uint32_t)(s->period_frac << shift))

                    div += 1;

            }

            counter = rem / div;

        }

    } else {

        counter = s->delta;

    }

    return counter;

}

void ptimer_set_count(ptimer_state *s, uint64_t count)

{

    s->delta = count;

    if (s->enabled) {

        s->next_event = qemu_get_clock_ns(vm_clock);

        ptimer_reload(s);

    }

}

void ptimer_run(ptimer_state *s, int oneshot)

{

    if (s->enabled) {

        return;

    }

    if (s->period == 0) {

        fprintf(stderr, "Timer with period zero, disabling\n");

        return;

    }

    s->enabled = oneshot ? 2 : 1;

    s->next_event = qemu_get_clock_ns(vm_clock);

    ptimer_reload(s);

}

/* Pause a timer.  Note that this may cause it to "lose" time, even if it

   is immediately restarted.  */

void ptimer_stop(ptimer_state *s)

{

    if (!s->enabled)

        return;

    s->delta = ptimer_get_count(s);

    qemu_del_timer(s->timer);

    s->enabled = 0;

}

/* Set counter increment interval in nanoseconds.  */

void ptimer_set_period(ptimer_state *s, int64_t period)

{

    s->period = period;

    s->period_frac = 0;

    if (s->enabled) {

        s->next_event = qemu_get_clock_ns(vm_clock);

        ptimer_reload(s);

    }

}

/* Set counter frequency in Hz.  */

void ptimer_set_freq(ptimer_state *s, uint32_t freq)

{

    s->period = 1000000000ll / freq;

    s->period_frac = (1000000000ll << 32) / freq;

    if (s->enabled) {

        s->next_event = qemu_get_clock_ns(vm_clock);

        ptimer_reload(s);

    }

}

/* Set the initial countdown value.  If reload is nonzero then also set

   count = limit.  */

void ptimer_set_limit(ptimer_state *s, uint64_t limit, int reload)

{

    /*

     * Artificially limit timeout rate to something

     * achievable under QEMU.  Otherwise, QEMU spends all

     * its time generating timer interrupts, and there

     * is no forward progress.

     * About ten microseconds is the fastest that really works

     * on the current generation of host machines.

     */

    if (limit * s->period < 10000 && s->period) {

        limit = 10000 / s->period;

    }

    s->limit = limit;

    if (reload)

        s->delta = limit;

    if (s->enabled && reload) {

        s->next_event = qemu_get_clock_ns(vm_clock);

        ptimer_reload(s);

    }

}

const VMStateDescription vmstate_ptimer = {

    .name = "ptimer",

    .version_id = 1,

    .minimum_version_id = 1,

    .minimum_version_id_old = 1,

    .fields      = (VMStateField[]) {

        VMSTATE_UINT8(enabled, ptimer_state),

        VMSTATE_UINT64(limit, ptimer_state),

        VMSTATE_UINT64(delta, ptimer_state),

        VMSTATE_UINT32(period_frac, ptimer_state),

        VMSTATE_INT64(period, ptimer_state),

        VMSTATE_INT64(last_event, ptimer_state),

        VMSTATE_INT64(next_event, ptimer_state),

        VMSTATE_TIMER(timer, ptimer_state),

        VMSTATE_END_OF_LIST()

    }

};

ptimer_state *ptimer_init(QEMUBH *bh)

{

    ptimer_state *s;

    s = (ptimer_state *)g_malloc0(sizeof(ptimer_state));

    s->bh = bh;

    s->timer = qemu_new_timer_ns(vm_clock, ptimer_tick, s);

    return s;

}